1. Field of the Invention
The present invention relates generally to an apparatus and method for installing an improved transition end, such as a threaded metal fitting, onto a terminating end of a plastic pipe in order to connect the plastic pipe to other associated metal components.
2. Description of the Prior Art
There is an ever increasing need for providing reliable interconnections between plastic pipe and metal components. As one example, modern water wells are drilled into the ground with the well bore either being uncased, or being protected by a casing which is sunk into the well. Typically, a submersible pump is then installed in the well bore on either rigid or flexible tubing and submerged in water located at the bottom of the well. The pump provides water to the surface through the flexible tubing which is connected to the pump and which leads up the well bore to the well surface. Although various types of flexible tubing are known, the most commonly used tubing today is a polyolefin, such as polyethylene. At the well surface, it is generally necessary to transition the plastic pipe to a metal coupling which, in turn, allows the pipe to be connected to metal components in the flow line.
Another example of the need for such a transition end on plastic pipe exists in the area of natural gas production and transmission lines. Modern gas utilities have broadly adopted plastic pipe for use with underground natural gas distribution and transmission systems. For example, in the supplying of natural gas, it is customary, at the present time, that the main lines located in the street are constructed of steel whereas feeder or service lines to houses and adjacent buildings are most frequently constructed of a plastic, such as polyethylene. Also, it is required that steel pipe be used above ground in making connections to gas regulators and meters, which frequently interconnect the underground plastic pipe to the main via so-called “risers”. Still further, steel line extensions commonly join to plastic mains. Consequently, many local and state governmental regulatory agencies have adopted safety codes which require above ground gas meter risers to be constructed of relatively rigid and durable metallic materials which protect against deterioration and external damage of an otherwise plastic riser assembly. Therefore, it is necessary to transition such subterranean plastic pipe to metallic risers for above ground use. In each of these situations, it is necessary to provide a suitable transition fitting that will accommodate both the plastic pipe and associated steel components.
A number of different techniques and devices have been used in the past to accomplish this task. For example, U.S. Pat. No. 6,896,297 to Central Plastics Company shows a device in which an internal stiffener sleeve is inserted within the plastic pipe in order to secure a surrounding metal transition end to a short section of pipe. The disadvantage of the technique shown in this patent is that the technique is not practical for a typical field installation since the section of plastic pipe with the transition end attached would then have to be butt welded to the remaining length of the plastic pipe, as well as presenting other complications.
U.S. Pat. No. 5,367,756 and U.S. Pat. No. 5,590,914 both show what appear to be related approaches to solving the problem. They are inserting a stiffener sleeve from the exterior of the metal pipe end, rather than from the interior of the plastic pipe. However, they appear to be installing the stiffener sleeve by forcing it downwardly into the mouth of the metal pipe and plastic pipe throat. It also appears that the stiffener sleeve used with the '914 and '756 patents is a relatively complex assembly and produces a poorly installed end.
U.S. Pat. No. 6,237,963 shows a device and method which are used in solving the same general type of problem but the steel pipe 11 is swaged down during the process to form a swage groove around the retainer sleeve, thereby compressing the gasket located there between.
U.S. Pat. No. 4,715,624 uses a specially designed piston which allows some movement between the plastic and steel components to relieve thermal stress. The patent actually teaches that it is disadvantageous to provide a compression fitting where the plastic is compressed because of the tendency to cold flow with a resulting reduction in holding strength over time (see column 1, lines 40-49).
While the above patents are representative of the advances which have been made in the prior art, there remains a need for further improvements. For example, it would be advantageous to provide a method using an apparatus for attaching a metal transition end to a section of plastic pipe or other pipe of the type used in submersible pump system in which an internal stiffener is installed from the open plastic pipe end rather than from the opposite end of the length of plastic pipe.
This type of method and apparatus could be used for field assemblies and would not require butt welding of sections of plastic pipe, since the internal stiffener is installed from the open plastic pipe end, rather than being inserted and then either pushed or pulled into position from the interior of the opposite end of the plastic pipe.